In brake boosters an input force is normally transmitted from a brake pedal through an input push rod to operate a valve arrangement. The valve arrangement controls the communication of fluid through which a pressure differential is created to develop an output force for effecting a brake application. The input push rod between brake pedal and valve is defined by a solid shaft having an eye on one end and a semi-spherical ball on the other end to provide for rotational movement of the brake pedal. With such an input push rod, the input force is communicated to a plunger of the valve arrangement along a linear path without the introduction of side forces that could effect a smooth operation of the brake booster. Because of strength requirements, the input push rod is normally made from a forged steel rod to transmit the operational input force that may be applied to effect a brake application. In an effort to reduce the overall weight of a brake booster, it has been suggested that an input push rod may be constructed of two different materials in U.S. Pat. Nos. 4,901,426; 5,230,134 and 5,606,790 to reduce weight and yet retains the strength requirements. While a two piece push rod may provide an option with respect to a one piece push rod, such a combination has not been accepted by the industry for use in a commercial brake booster.
A primary object of the present invention is to fabricate a push rod for a brake booster from a light weight cylindrical tube to provide a link between a brake pedal and a plunger of a valve arrangement.
According to this invention, a cylindrical tube is cut to a desired length from a source of supply. The cylindrical tube is transmitted to a first station and placed in a die where a first axial force is applied to a first end of the cylindrical tube and a second axial force is applied to a second end causing a portion of the cylindrical tube there between to be up-set into a cavity to form an external annular rib between the first end and the second end. Thereafter, the cylindrical tube is held stationary and a first annular groove is rolled into the cylindrical tube mid-way between the rib and the second end of the cylindrical tube and a second annular groove is rolled into the cylindrical tube adjacent the second end. The area between the first and second annular grooves defining an internal socket for receiving a spherical head on a plunger for a brake booster. Subsequently, opposite first and second radial forces are applied to a portion of the cylindrical tube adjacent the first end to flatten the cylindrical tube adjacent the first end into a substantially rectangular body. Then a hole that is perpendicular to the cylindrical tube is drilled or punched into the rectangular body. The hole receives a pin to connect the cylindrical body with a pedal pedal for applying an input force to move a plunger of a valve arrangement in a brake booster. This first embodiment of the input push rod may now be connected to a plunger for use in a valve arrangement of a brake booster. A poppet valve and return spring is located on the first end second end of the cylindrical tube and a force is applied to push a semi-spherical ball into the socket, The poppet valve and spring is compressed and a force is applied to crimp the first end around the semi-spherical head to join the cylindrical tube to the plunger for later installation into a valve body of a brake booster. This first embodiment of the input push rod requires equipment to be available to crimp the cylindrical tube to a valve plunger and as such equipment may not always be available the installation sequence differ a second embodiment of the invention provides a different option for joining the cylindrical tube to a plunger by rolling a second annular groove into the cylindrical tube adjacent the second end, cutting a plurality of slits cut from the second end toward the first annular groove to form a plurality of arcuate fingers and rolling a flange from the second annular groove to the second end. In this embodiment, after the return spring and poppet valve have been placed on the second end a force is applied to press semi-spherical ball on the plunger into the socket, the plurality of fingers flex to allow the semi-spherical ball to be resiliently held in the socket to join the cylindrical tube with the plunger. In any event, an input force applied through the pin connection on the first end is carried as a linear force through the cylindrical tube into the plunger to activate the valve arrangement and effect a brake application.
An advantage of this invention resides in a push rod defined by a cylindrical tube through which a linear force is applied to activate a plunger of a valve arrangement to effect the development of pressure differential in a brake booster during a brake application.